Energy absorbing system

ABSTRACT

A heavy duty ground retractable automobile barrier for a railroad crossing. Concrete bunkers are placed at each side of a roadway. An upstanding concrete-filled steel pipe fixed in each bunker has a sleeve for rotational and axial movement. Shock absorbers are mounted on each sleeve. A net extends across the road and is attached to the opposite ends of the shock absorbers. Collision of an automobile with the net creates tensile forces in the net. The shock absorbers expand while rotating about the pipe&#39;s axis in response to tensile forces from the net that meet or exceed a minimum threshold. Forces from the net pass through the axis of the steel pipe. The net is stored in a pit transverse the roadway parallel to the railroad tracks and is raised and lowered as appropriate. The net includes a cable that extends across the road in a wave pattern, having peaks, valleys and midpoints, wherein tangents of the wave midpoints are at least 90 degrees from tangents of the peaks and valleys.

BACKGROUND OF THE INVENTION

[0001] This invention relates to an energy absorbing system that can beused to dissipate unwanted energy such as, e.g., the energy of an errantvehicle. The system can be used in a variety of applications, includingHOV lane traffic control, drawbridges, security gates, or crash cushionapplications. In one application, the system is used to prevent avehicle from crossing a railroad track while the warning gates are downor there is a train in the area.

[0002] The problem of vehicles improperly crossing railroad tracks isbecoming more pronounced due to a rise in both the average speed oftrains and in the number of vehicles on the roads. For example, a newhigh speed rail line has recently been put into service on the eastcoast of the United States, which passes through densely populatedareas. Traditional systems for preventing vehicles from crossing thetracks at inopportune times have proved less than fully satisfactory.Traditional gates can be bypassed by impatient drivers who don't yet seea train coming, and, in any event, will not stop a vehicle that is outof control.

[0003] Other vehicle barriers have been proposed, but none have solvedthe problem in a manner that is both feasible and commerciallypractical. Thus, old-fashioned gates are still the most common systemfor protecting railroad crossings.

SUMMARY OF THE INVENTION

[0004] In one aspect, an energy absorbing system according to thepresent invention includes a stanchion, a bearing sleeve rotatable andvertically slidable on the stanchion, one or more hydraulic shockabsorbers in its compressed state connected to the sleeve, a thresholdforce securing mechanism connected to the shock absorbers, and a groundretractable restraining net connected to the shock absorbers, whereinthe securing mechanism prevents expansion of the shock absorbers untilacted upon by tensile forces of at least a minimum threshold force,wherein the minimum threshold force exceeds a static tensile forceexerted by the restraining net in a quiescent state upon the shockabsorber, and wherein the minimum threshold force is less than dynamictensile forces that the net would exert on the shock absorber when anautomobile collides with the net at substantial speed.

[0005] In another aspect, an energy absorbing system according to thepresent invention includes a fixing means for fixing a vertical axis, ashock absorbing means connected to the fixing means, for absorbingtensile forces while rotating around the vertical axis, and a thresholdforce securing means connected to the shock absorbing means, forpreventing expansion of the shock absorbing means until acted upon bytensile forces of at least a minimum threshold force. Preferably, theshock absorbing means is connected to a rotating means for rotatingabout the fixing means and/or axis. The rotating means may be a bearingsleeve, for example. The energy absorbing system may further comprise atorque protection means for adding structural strength to the shockabsorbing means to resist deformation due to the torque upon the shockabsorbing means. A restraining means may be connected to the shockabsorbing means, for absorbing forces and for transferring forces to theshock absorbing means, and through the shock absorbing means to thesupport means. The restraining means may include a restraining net ornet means. It preferably comprises horseshoe cable, or cable extendingsubstantially horizontally in a wave pattern with vertical amplitude,having peaks, valleys and midpoints, wherein tangents of the wavemidpoints are at least 90 degrees from tangents of the peaks andvalleys.

[0006] In yet another aspect, an energy absorbing system according tothe present invention includes a stanchion, a bearing sleeve rotatableand vertically slidable on the stanchion, a shock absorber connected tothe sleeve, and a shear pin connected to the shock absorber whichprevents expansion of the shock absorber until acted upon by tensileforces of at least a minimum threshold force. Preferably, the minimumthreshold force is about 3,000 to about 15,000 pounds. Most preferably,the minimum threshold force is about 5,000 to about 10,000 pounds. Theenergy absorbing system may include wheels and a cross-bar between atleast two shock absorbers on a stanchion, supporting the shockabsorbers.

[0007] In a further aspect, an energy absorbing system according to thepresent invention includes a stanchion, a bearing sleeve rotatable andvertically slidable on the stanchion, a shock absorber connected to thesleeve, a restraining net connected to the shock absorber, and a shearpin connected to the shock absorber which prevents expansion of theshock absorber until acted upon by tensile forces of at least a minimumthreshold force. Preferably, the restraining net in a quiescent stateexerts a static tensile force upon the shock absorber, and the minimumthreshold force exceeds the static tensile force. The net preferablyextends across a roadway and is ground retractable. The net preferablycomprises horseshoe cable, or cable extending substantially horizontallyin a wave pattern with vertical amplitude, having peaks, valleys andmidpoints, wherein tangents of the wave midpoints are at least 90degrees from tangents of the peaks and valleys.

[0008] In a still further aspect, a restraining net according to thepresent invention includes top, middle and bottom horizontally extendingstructural cables, and horseshoe cable extending along and between thehorizontally extending cables, or cable extending substantiallyhorizontally along the horizontally extending structural cables in awave pattern with vertical amplitude, having peaks, valleys andmidpoints, wherein tangents of the wave midpoints are at least 90degrees from tangents of the peaks and valleys.

[0009] In yet another aspect, a railroad crossing safety systemaccording to the present invention includes a roadway, railroad trackscrossing the roadway, first and second energy absorbing systemsinstalled respectively on each side of the roadway, ground retractablerestraining means for restraining automobiles from crossing the railroadtracks, the restraining means extending across the roadway between thefirst and second energy absorbing systems on each side of the railroadtracks, each of the first and second energy absorbing systems comprisingsupporting means for providing a rigid support for a fixing means,fixing means for rigidly fixing a vertical axis relative to thesupporting means, shock absorbing means for absorbing forces applied tothe shock absorbing system, the shock absorbing means being mounted onthe fixing means to rotate around the vertical axis, and a thresholdforce securing mechanism connected to the shock absorber preventingexpansion of the shock absorber until acted upon by tensile forces of atleast a minimum threshold force, wherein the restraining means compriseshorseshoe cable.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1A is a perspective view which illustrates a railroadcrossing for a multi-lane roadway with one embodiment of the inventioninstalled and restraining an automobile;

[0011]FIG. 1B is a perspective view which illustrates a railroadcrossing for a multi-lane roadway with a preferred embodiment installedand restraining an automobile;

[0012]FIG. 2A is a top view, partially cut away, of an embodiment as itwould appear on one side of the railroad track;

[0013]FIG. 2B is a side view, partially in section, of a net slot, abunker, a net, a stanchion, and a net raising and lowering mechanism,which includes a pair of hydraulic shock absorbers with threshold forcesecuring mechanism, with wheels and a vertical cross-bar to support theshock absorbers;

[0014]FIG. 2C is a side view, partially in section, of a net slot, abunker, a net, a stanchion, and a net raising and lowering mechanism,which includes a pair of hydraulic shock absorbers with threshold forcesecuring mechanism, without wheels and a vertical cross-bar to supportthe shock absorbers;

[0015]FIG. 3A is a top view of a second embodiment as it would appear onone side of the railroad track;

[0016]FIG. 3B is a side view of a second embodiment as it would appearon one side of the railroad track, with wheels and a vertical cross-barto support the shock absorbers;

[0017]FIG. 3C is a side view of a second embodiment as it would appearon one side of the railroad track, without wheels and a verticalcross-bar to support the shock absorbers;

[0018]FIG. 4A is a sectional view of a stanchion with sleeve and netraising and lowering jacks;

[0019]FIG. 4B is a side view of a stanchion with sleeve and net raisingand lowering jacks;

[0020]FIG. 5 is an exploded, perspective view of a stanchion with sleeveand shock absorbers with threshold force securing mechanism;

[0021]FIG. 6A is a side view of a preferred embodiment of a hydraulicshock absorber with shear pins to act as threshold force securingmechanism, shown partially cut away and in its quiescent state;

[0022]FIG. 6B is a side view of a preferred embodiment of a hydraulicshock absorber with shear pins to act as threshold force securingmechanism, shown partially cut away and in its expanded state after avehicular collision with the net;

[0023]FIG. 7A is a side view of a second preferred embodiment of ahydraulic shock absorber with shear pins to act as threshold forcesecuring mechanism and a torque protection structure, shown partiallycut away and in its quiescent state;

[0024]FIG. 7B is a side view of a second preferred embodiment of ahydraulic shock absorber with shear pins to act as threshold forcesecuring mechanism and a torque protection structure, shown partiallycut away and in its expanded state after a vehicular collision with thenet; and

[0025]FIG. 8 is an expanded side view of a net according to oneembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The energy absorbing system in one aspect of a preferredembodiment comprises a stanchion or other mechanism for providing afixed vertical axis, shock absorbing mechanisms mounted on the stanchionfor absorbing forces, and a restraining net or other barrier connectedto the shock absorbing mechanism. The shock absorbing mechanism ispreferably mounted for rotation about the axis, is linearly translatablein a direction parallel to the axis, and is expandable in a directionsubstantially orthogonal to the axis.

[0027] Preferably, the shock absorbing mechanism is a hydraulic shockabsorber with a securing mechanism such that the piston does not expandexcept in response to tensile forces that meet or exceed a minimumthreshold force. In one aspect, it is envisioned that static tensionfrom the restraining net in its quiescent state would not exceed thisminimum threshold force, but that increased tension due to the dynamictensile forces exerted upon the shock absorber from an automobiledriving into the restraining net would exceed this minimum thresholdforce.

[0028] In accordance with other embodiments, a restraining net comprisestop, middle and bottom horizontally extending structural cables. Cablearranged in horseshoe-curves extends along and among the horizontallyextending cables. The term “horseshoe-curve” includes a curve in theform of a wave with a plurality of horseshoe-shaped peaks and aplurality of horseshoe-shaped valleys. It has been found that such cablehas improved capturing ability. In preferred embodiments, this cableextends substantially horizontally in a wave pattern with verticalamplitude (similar to a sine wave), having peaks, valleys and midpoints,wherein tangents of the wave midpoints are at least 90 degrees fromtangents of the peaks and valleys, as is explained further below.

[0029] Referring to the drawings, wherein like reference numeralsrepresent identical or corresponding parts throughout the several views,and more particularly to FIG. 1, a general layout of an embodiment isshown installed at a typical railroad crossing. A roadway is indicatedgenerally by reference numeral 10 and railroad tracks are indicatedgenerally by reference numeral 12. A pair of capture nets 20 arestretched across roadway 10 parallel to tracks 12. Each capture net 20extends between a pair of housings 22 located on opposite sides ofroadway 10. The net 20 is connected at each end to shock absorbers whichin turn are connected to, or may be considered part of, mechanisms forraising and lowering nets 20, as described in greater detailhereinafter. The mechanisms may be entirely contained in the housings.Alternatively, the mechanisms may protrude from the housings as shown inFIG. 1. Alternatively, the housings may be omitted altogether. Themechanisms are under the control of a standard train-detecting system,such as is commonly used to control gates at railroad crossings. Eachhousing 22 covers a support 28 which provides support and stability.

[0030] Preferably, each net 20 is normally stored in a slot 24 thatextends transversely across roadway 10 between housings 22. Shown at thetop of FIG. 1 is a vehicle 26 which has crashed into net 20 and isrestrained by net 20 to prevent it and its occupants from encroachingonto tracks 12 when the train passes through. Top net 20 has beendeflected by the collision from its quiescent state so as to form ashallow “V” shape. The ability to be deflected, yet provide arestraining force, allows vehicle 26 to be progressively stopped,thereby lessening adverse effects of the impact forces acting on vehicle26 and its occupants. The deflecting and restraining functions areachieved by a unique energy absorbing system, to be described in greaterdetail hereinafter.

[0031] A top view is shown in FIG. 2A with roadway 10 and housings 22removed. FIG. 2B shows a side view along the lines 2B-2B of FIG. 2A.FIG. 2C shows a similar view. Support 28 comprises a concrete bunker 30and a stanchion 32. Stanchion 32 is a structure for rigidly fixingvertical axis 52. Bunker 30 may be poured at the site, or it may befabricated elsewhere and installed at the site, on each side of roadway10 and comprises a foundation 34 and upstanding bunker walls 36. Walls36 define in bunker 30 a pit 38 which is open upwardly toward roadway10. Foundation 34 may typically, for example, be from two to twelve feetwide and from three to nine feet deep. The top 40 of walls 36 arepreferably about six inches above ground level 42 to provide aprotective curb around bunker 30. A sump pump 44 is preferably providedto remove any water which might accumulate in pit 38 into a drainagepipe 46.

[0032] Stanchion 32, which may comprise a twenty-five inch steel pipe48, is filled with concrete 50 and is preferably embedded approximatelyfour feet deep in foundation 34 at the bottom of pit 38 and extends fiveto six feet above the top of foundation 34. Stanchion 32 has a verticalaxis 52, whose function will become clear hereinafter. Foundation 34 andwalls 36 may be of solid concrete. Because of the size and mass of thesupport 28, it provides a solid support which resists forces imposedupon it.

[0033] Also typically at the site is a concrete roadway foundation 54which extends across roadway 10 to another bunker 30, not described indetail, since all bunkers 30 may be identical. Roadway foundation 54preferably includes at least one key slot 56 which comprises a recess ofany convenient size and shape.

[0034] Roadway foundation 54 supports a pair of pre-cast, concretestructures 58, 58′ which comprise the net slots 24, 24′ in the roadwayinto which net 20 is lowered for storage. As shown in FIGS. 2B and 2C,the top 60 of net slots 24, 24′ are at ground level 42, so that they areflush with the surface of roadway 10. Structures 58, 58′ formessentially a pair of net slots 24, 24′ which are shown end to end inFIGS. 2A-2C. Each of structures 58, 58′ are substantially U-shapedhaving a base 62, 62′ and a pair of upstanding arms 64, 64′ definingslots 24, 24′. Inasmuch as concrete structures 58 and 58′ are mirrorimages, otherwise being identical, the following explanation ofstructure 58 is also applicable to 58′. An example net slot 24 is shownin cross-sectional view in FIG. 8 of U.S. Pat. No. 5,762,443 to Gelfandet al., incorporated herein by reference.

[0035] The partial cross-section shown in FIGS. 2B and 2C bisects slot24 and pit 38. The upper surface of base 62 slopes toward pit 38 topermit runoff from accumulating in slot 24, where it might freeze andcause an obstruction. Note that the slopes shown in FIGS. 2B and 2C maybe decreased. The concrete structures 58 that form net slots 24 may bepre-cast elsewhere and then transported to the site. Base 62 of net slot24 preferably has at least one downwardly extending key 66 which is of acomplementary size and shape to key slot 56. Key 66 aids in aligning thesystem with roadway foundation 54 and resists any shearing movement ofconcrete structure 58 relative to roadway foundation 54. After key 66has been fit into key slot 56, key slot 56 is preferably grouted solid.Pre-casting the concrete structure 58 and providing it with key 66simplifies the construction at the site, thereby reducing constructioncosts.

[0036] As shown in FIGS. 2B and 2C, respectively, the energy absorbingsystem may be provided with or without wheels 80 and a verticalcross-bar 82 between the shock absorbers to support the shock absorbers.The cross-bar may also alleviate vertical torque on the shock absorbers,which might otherwise occur due to the fact that a vehicle collidingwith the net causes the top and bottom cables (and therefore the shockabsorbers) to tend to squeeze together. Thus, the cross-bar may act as astabilizer against this vertical torque. The wheels 80 and cross-bar 82are particularly preferred when the shock absorbers 84 are long and/orheavy. Although the wheels 80 and cross-bar 82 are shown in the netconfiguration comprising horseshoe cable, it is understood that they maybe employed in other net configurations, including the configurationshown in FIG. 1A. In addition, one may readily appreciate that skidplates or other supporting means may be used in combination with, or asa replacement for the wheels.

[0037] Referring to FIGS. 4, 5, 6 and 7, a preferred embodiment of theenergy absorbing system comprises a bearing sleeve 72 which is rotatableand vertically slidable on stanchion 32, and a pair of shock absorbers84 mounted on bearing sleeve 72 by securing shock absorber flange 114 tobearing sleeve flange 116. The shock absorbers 84 are equipped with athreshold force securing mechanism, as described in more detail below.

[0038] Stanchion 32 is embedded in foundation 34, thereby rigidly fixingin concrete the location of vertical axis 52. Slidable vertically onstanchion 32 is bearing sleeve 72. Preferably, as seen in FIGS. 4 and 5,bearing sleeve 72 comprises a galvanized steel sleeve 74 with a lubritebronze insert 76 press fit therewithin which is reamed to fit externallymilled stanchion 32. In FIG. 5, insert 76 is shown separate from steelsleeve 74. Mounted on bearing sleeve 72, one above the other, are twoshock absorbing mechanisms 84 (FIG. 5).

[0039] The housing 110 of each shock absorbing mechanism 84 is fixed tosteel sleeve 74, and its piston 112 is connected to net 20. Theconnection shown in FIGS. 3 and 8 are but exemplary of the many ways ofattaching net 20 to piston 112.

[0040] In one embodiment, shock absorber 84 is hydraulic with about a50,000 pound resistance with a twelve inch stroke and an accumulatorwith a 5,000 pound return force. In a another embodiment, shock absorber84 is hydraulic with about a 20,000 pound resistance with a four footstroke and an accumulator with a 5,000 pound return force.

[0041] As best seen in FIG. 5, steel sleeve 74 has flanges 116 whichconnect to shock absorber flange 114. Shock absorber cylinder 110 isremovably mounted thereto by flanges 114. Shock absorber piston 112 isremovably attached to the net 20. In one embodiment, the attachment iseffected by means of a threaded extension 118 of piston 112 which isreceived in an internally threaded sleeve-bolt (not shown) attached tothe net 20. Preferably, the attachment is effected by means of an eyeletextension 119 of piston 112, as shown in FIGS. 6-7, through which acable, clamp or other appropriate securing mechanism may be passed inorder to secure the net 20 to the piston 112.

[0042]FIGS. 6A and 6B illustrate a preferred embodiment of the shockabsorbing mechanism. Shock absorbers 84 are shown in their quiescentstate and their expanded state, respectively. Being top views, only thetop shock absorber 84 is seen, the other lying directly beneath the onevisible. In the quiescent state (FIG. 6A), net 20 is stretchedtransversely across roadway 10 in the manner exemplified by bottom net20 in FIG. 1. As shown in FIG. 6A, net 20 has not yet been subject tocollision with a vehicle.

[0043] Shock absorber 84 is normally in a compressed state, secured by athreshold force securing mechanism. The mechanism is capable ofwithstanding a threshold tensile force. In one embodiment, a thresholdforce securing mechanism includes a series of shear pins 100 insertedthrough a shear pin collar 101 into a shear pin ring 102. The shear pincollar 101 may be integral or separate from other parts of the shockabsorber. The shear pin optionally may be secured by a set screw 103.One can readily envision other threshold force securing mechanisms thatmay be used in combination with, or instead of, a shear pin. For examplea securing mechanism such as a brake pad, or a counterweight, or othercounter-force may be used. The threshold force securing mechanism allowsthe shock absorber 84, without expanding from its compressed state, topull net 20 taut. The shock absorber on the other side of roadway 10, inan identical configuration, will pull the other side of the net 20 taut.Typically, capture net 20 is installed with a 5,000-10,000 poundpre-tension horizontal load on its cables.

[0044] When an automobile 26 collides with net 20, the automobiledeflects the net, causing it to exert a tensile force exceeding theminimum threshold force upon shock absorber 84. When the threshold forcemeans includes shear pins, the tensile force causes the pins to shearand thereby permits the expansion of piston 112 of shock absorber 84against the resistance of the hydraulic fluid in cylinder 110 (FIG. 6B).Shock is thereby absorbed during its expansion, while the force of thenet 20 also rotates shock absorber 84 and bearing sleeve 72. Forcesapplied upon net 20 are thereby translated through the center ofstanchion 32, which is solidly anchored in foundation 34. Energy isdistributed among and absorbed by the net 20, the shock absorbers 84 andthe stanchion 32. This permits a relatively compact size while beingeffective in resisting applied forces.

[0045] A second embodiment of the shock absorbing mechanism includes atorque protection structure. In a preferred aspect as illustrated inFIGS. 7A and 7B, shock absorbers 84 include a protective sleeve 111which adds structural strength to resist deformation of the housing 110or other parts of the shock absorber 84 due to the torque that the net20 exerts upon capturing an automobile and deflecting shock absorbers84. The protective sleeve 111 may be made of any suitable structuralmaterial, but is preferably aluminum or steel.

[0046] Referring to FIGS. 1, 3, and 8, the restraining mechanismincludes a net 20 comprising a plurality of horizontally extendingstructural cables 136 made of one inch galvanized structural strandswith a breaking strength of sixty-one tons or more. In one embodiment ofthe restraining mechanism, the structural cables 136 are connected by aplurality of vertically extending cables 138, as shown in FIG. 1A. Thesevertical cables 138 are preferably five-eighths inch galvanizedstructural strands with a minimum breaking strength of twenty-four tons,connected to horizontal strands 136 through swaged sockets.

[0047] In another embodiment of the restraining mechanism, thestructural cables 136 are connected by horseshoe cable 138, as shown inFIGS. 1B, 3 and 8. Preferably, the horseshoe cable comprises wire ropeand may be secured to the structural cables by wire rope cable clamps140. The horseshoe cable may comprise a plurality of cables, but it ispreferred that it be more unitary. The horseshoe cable design providesexemplary automobile capturing properties by allowing the net to wraparound the automobile, preventing it from slipping over the net. As seenin FIGS. 1B, 3 and 8, the cable extends substantially horizontally in awave pattern with vertical amplitude, having peaks, valleys andmidpoints. In the embodiment shown in these figures, the peaks arelocated at the top horizontal cable, the valleys are located at thebottom horizontal cable, and the midpoints are located at the middlehorizontal cable. It is evident from the figures that the tangents ofthe wave midpoints are more than 90 degrees from tangents of the peaksand valleys.

[0048] Returning to FIGS. 4A and 4B, a preferred form of the liftmechanism will now be described. Steel sleeve 74 of bearing sleeve 72has integrally fixed thereto a lift flange 154, shown as circular inFIGS. 4 and 5, but which could be of any suitable configuration. It isconvenient and practical to make bearing sleeve 72 complete at thefactory. Bronze insert 76 is press-fit into steel sleeve 74 and reamedto size, and flanges 116 and 154 are welded to sleeve 74. The unit isthen ready to be brought to the site and simply installed on steel pipe48 which was previously milled to mate with insert 76.

[0049] Lift flange 154 rests on caps 156 of lifting screws 158 oflifting jacks 160. Lifting jacks 160 should preferably be capable ofsupporting a minimum of 5,000 pounds at a screw extension of forty-eightinches and are supplied with motors 162 (FIG. 2) and speed reducers (notshown) which are preferably capable of lifting 3500 points per jackforty-eight inches in twenty seconds. The operation of lifting jacks 160can conveniently be synchronized through the use of rotary limitswitches. Lifting jacks 160 are mounted on base plate 164. Base plate164 can desirably be welded to steel pipe 48. Integrally depending frombase plate 164, and thereby controllably spaced appropriately, are apair of three inch steel pipes 166 which provide pockets 168 for liftingscrews 158. Integrally constructing pipe 48, base plate 164, and pipes166 prior to removal to the site also simplifies on-site construction,for they can be brought to the site as a unit and simply dropped intoplace. Even more preferably, the unit may be pre-installed (off-site) inbunker 30 which itself may be brought to the site and installed.

[0050] Housing 22 is shown in FIG. 1 is preferably a prefabricatedenclosure with stainless steel outer panels so that it can withstandeven the most rigorous of weather conditions. The side panels of housing22 may be hinged for easy access, or housing 22 may be a unitaryenclosure which is removable from bunker walls 36. Within housing 22, astainless steel roll up door (not shown) may be included, which israised by net 20 and which closes automatically due to gravity.

[0051] In operation, a control system (not disclosed) will sense thepresence of an oncoming train and will thereby control net operations.Lift motors 162 will be synchronously actuated so that lift screws 158of lift jacks 160 will raise bearing sleeve 72 and therewith net 20.Should a vehicle crash into net 20, net 20 will deflect, rotating shockabsorbing mechanisms 78 about axis 52 of stanchion 32 and expandinghydraulic shock absorbers 84 to restrain the vehicle. The restrainingforces will act through axis 52, placing the strain upon a concretefilled steel pipe embedded solidly in a concrete foundation. After thetrain passes, the control system will reverse motors 162 to lower net 20into slot 24 of concrete structure or net slot 58.

[0052] In addition to railroad crossings, the system can also be used ina variety of other applications, including HOV lane traffic control,drawbridges, security gates, or crash cushion applications. One canreadily appreciate that the control system for such applications maydiffer from that used in a railroad crossings. At security gates, forexample, the restraining net or other barrier would normally be in araised position, and actuation of the security system (e.g., by a guard,a key card, keyboard punch, etc.) would lower the barrier and permitpassage.

EXAMPLE

[0053] An embodiment similar to that shown in FIGS. 3A and 3B wasconstructed without ground retractability, as follows. The overall widthof the installation was 18.4 m (60.4 ft) centerline to centerline of thestanchions. The net width was 10.5 m (34.5 ft). The uninstalledconstructed net height was 0.9 m (3.0 ft). The height of the net wheninstalled and tensioned was 1.0 m (3.3 ft) to the center of the topcable and 0.2 m (0.7 ft) to the center of the bottom cable as measuredat the centerline of the net assembly. A measure of the tension wasrecorded in the top and bottom cables of 27.5 kN (6182.3 lb) and 17.5 kN(3934.2 lb), respectively.

[0054] The cable net was constructed of three equally spaced horizontalmembers. The top and bottom horizontals were 19 mm (0.8 in) diameterExtra High Strength (EHS) wire strand. The center horizontal was 16 mmdiameter 6×26 wire rope. The horseshoe cable net members were fabricatedof a single 16 mm (0.6 in) diameter 6×26 wire rope. The wire rope waswoven up and down along the net width and attached to the top and bottomhorizontal wire strand members with three 19 mm (0.8 in) cable clamps ateach location and a single 32 mm (1.3 in) modified cable clamp where therope passed over the center strand. The ends of the top and bottomstrands were fitted with Preformed Line Products™ 1.8 m (6.0 ft) BigGrip Dead Ends. The net was attached on one side to shock absorbers witha 32 mm (1.3 in)×457 mm (18 in) turnbuckle and 19 mm (0.8 in) clevis atthe top and bottom horizontal strand locations. The opposing net end wasconnected to shock absorbers with a 19 mm (0.8 in) clevis at the top andbottom horizontal strand locations.

[0055] The stanchions were fabricated from two sections of steel pipe toform a rotating or hinged anchor system. The anchored inner section ofthe stanchion was fabricated from A36 steel pipe 305 mm (12.0 in) O.D.,25 mm (1.0 in) wall×1372 mm (54.0 in). Additionally, two 6 mm (0.25 in)rolled bronze plates were welded to each inner section to form bearings.A 6 mm (0.3 in) thick×54 mm (2.1 in) wide steel shelf ring was welded tothe perimeter of the inner section to vertically support the outersection 152 mm (6.0 in) above the roadway surface. The inner section wasfillet welded to a 25 mm (1.0 in)×686 mm (27.0 in)×686 mm (27.0 in)steel plate and anchored with sixteen 25 mm (1.0 in) mechanical anchors.The outer section was fabricated from A36 steel pipe 381 mm (15.0 in)O.D., 19 mm (0.8 in) wall×1372 mm (54.0 in).

[0056] The hydraulic shock absorber cylinders were 2.9 m (9.6 ft) longoverall. The effective piston stroke was 2.4 m (8.0 ft).

We claim:
 1. An energy absorbing system comprising: a stanchion; abearing sleeve rotatable and vertically slidable on the stanchion; ahydraulic shock absorber in its compressed state connected to thesleeve; a threshold force securing mechanism connected to the shockabsorber; and a ground retractable restraining net connected to theshock absorber; wherein the securing mechanism prevents expansion of theshock absorber until acted upon by tensile forces of at least a minimumthreshold force; wherein the minimum threshold force exceeds a statictensile force exerted by the restraining net in a quiescent state uponthe shock absorber; and wherein the minimum threshold force is less thandynamic tensile forces that the net would exert on the shock absorberwhen an automobile collides with the net at substantial speed.
 2. Anenergy absorbing system comprising: a fixing means for fixing a verticalaxis; a shock absorbing means connected to the fixing means, forabsorbing tensile forces while rotating around the vertical axis; and athreshold force securing means connected to the shock absorbing means,for preventing expansion of the shock absorbing means until acted uponby tensile forces of at least a minimum threshold force.
 3. The energyabsorbing system according to claim 2, wherein the shock absorbing meansis linearly translatable in a direction parallel to the vertical axis.4. The energy absorbing system according to claim 2, wherein the shockabsorbing means is expandable in a substantially orthogonal directionrelative to the vertical axis.
 5. The energy absorbing system accordingto claim 3, wherein the shock absorbing means is expandable in asubstantially orthogonal direction relative to the vertical axis.
 6. Theenergy absorbing system according to claim 2, wherein the shockabsorbing means is connected to a rotating means for rotating about thefixing means.
 7. The energy absorbing system according to claim 2,wherein the shock absorbing means has a 50,000 pound resistance.
 8. Theenergy absorbing system according to claim 7, wherein the shockabsorbing means has a twelve inch stroke.
 9. The energy absorbing systemaccording to claim 7, wherein the shock absorbing means has anaccumulator with a 5,000 pound return force.
 10. The energy absorbingsystem according to claim 9, wherein the shock absorbing means has a20,000 pound resistance.
 11. The energy absorbing system according toclaim 10, wherein the shock absorbing means has a four foot stroke. 12.The energy absorbing system according to claim 11, wherein the shockabsorbing means has an accumulator with a 5,000 pound return force. 13.The energy absorbing system according to claim 6, wherein the rotatingmeans is mounted on the fixing means.
 14. The energy absorbing systemaccording to claim 6, wherein the rotating means comprises a bearingsleeve.
 15. The energy absorbing system according to claim 2, furthercomprising a torque protection means for adding structural strength tothe shock absorbing means to resist deformation due to the torque uponthe shock absorbing means.
 16. The energy absorbing system according toclaim 6, further comprising a torque protection means for addingstructural strength to the shock absorbing means to resist deformationdue to the torque upon the shock absorbing means.
 17. An energyabsorbing system according to claim 2, comprising a restraining meansconnected to the shock absorbing means, for absorbing forces and fortransferring forces to the shock absorbing means, and through the shockabsorbing means to the support means.
 18. An energy absorbing systemaccording to claim 6 comprising a restraining means connected to theshock absorbing means, for absorbing forces and for transferring forcesto the shock absorbing means, and through the shock absorbing means tothe support means.
 19. An energy absorbing system according to claim 18,wherein the restraining means comprises a restraining net means.
 20. Anenergy absorbing system according to claim 18, wherein the restrainingmeans comprises horseshoe cable.
 21. An energy absorbing systemaccording to claim 18, wherein the restraining means comprises cableextending substantially horizontally in a wave pattern with verticalamplitude, having peaks, valleys and midpoints, wherein tangents of thewave midpoints are at least 90 degrees from tangents of the peaks andvalleys.
 22. An energy absorbing system according to claim 6, furthercomprising: a torque protection means for adding structural strength tothe shock absorbing means to resist deformation due to the torque upon the shock absorbing means, and a restraining means connected to the shockabsorbing means, for absorbing forces and for transferring forces to theshock absorbing means, and through the shock absorbing mean s to thesupport means.
 23. An energy absorbing system comprising: a stanchion; abearing sleeve rotatable and vertically slidable on the stanchion; ashock absorber connected to the sleeve; and a shear pin connected to theshock absorber which prevents expansion of the shock absorber untilacted upon by tensile forces of at least a minimum threshold force. 24.An energy absorbing system according to claim 23, further comprising abunker into which said stanchion is secured.
 25. An energy absorbingsystem according to claim 23, further comprising a foundation and a pipeembedded in the foundation.
 26. An energy absorbing system according toclaim 23, wherein the shock absorber is a hydraulic shock absorber. 27.An energy absorbing system according to claim 23, wherein the minimumthreshold force is about 3,000 to about 15,000 pounds.
 28. An energyabsorbing system according to claim 23, wherein the minimum thresholdforce is about 5,000 to about 10,000 pounds.
 29. An energy absorbingsystem according to claim 23, wherein the shock absorber comprises atorque protective sleeve comprised of a material selected from the groupconsisting of aluminum and steel.
 30. An energy absorbing systemaccording to claim 23, further comprising wheels and a cross-bar betweenat least two shock absorbers on a stanchion, supporting the shockabsorbers.
 31. A shock absorbing system, comprising: a stanchion; abearing sleeve rotatable and vertically slidable on the stanchion; ashock absorber connected to the sleeve; a restraining net connected tothe shock absorber; and a shear pin connected to the shock absorberwhich prevents expansion of the shock absorber until acted upon bytensile forces of at least a minimum threshold force.
 32. An energyabsorbing system according to claim 31, wherein the restraining net in aquiescent state exerts a static tensile force upon the shock absorber,and the minimum threshold force exceeds the static tensile force.
 33. Anenergy absorbing system according to claim 31, further comprising atorque protective sleeve attached to the shock absorber.
 34. An energyabsorbing system according to claim 31, wherein the net extends across aroadway and is ground retractable.
 35. An energy absorbing systemaccording to claim 31, wherein the net is adjacent to and approximatelyparallel to railway tracks.
 36. An energy absorbing system according toclaim 31, wherein the net comprises horseshoe cable.
 37. An energyabsorbing system according to claim 36, wherein the horseshoe cablecomprises wire rope.
 38. An energy absorbing system according to claim37, wherein the horseshoe cable is substantially unitary.
 39. An energyabsorbing system according to claim 31, wherein the restraining netcomprises cable extending substantially horizontally in a wave patternwith vertical amplitude, having peaks, valleys and midpoints, whereintangents of the wave midpoints are at least 90 degrees from tangents ofthe peaks and valleys.
 40. A restraining net comprising: top, middle andbottom horizontally extending structural cables; and horseshoe cableextending along and between the horizontally extending structuralcables.
 41. The restraining net according to claim 40, wherein thestructural cables comprise wire strand.
 42. The restraining netaccording to claim 40, wherein the top and bottom structural cablescomprise wire strand, and the middle horizontal cable comprises wirerope.
 43. The restraining net according to claim 40, wherein thehorseshoe cable comprises wire rope.
 44. The restraining net accordingto claim 40, wherein the top and bottom structural cables comprise wirestrand, the middle horizontal cable comprises wire rope, and thehorseshoe cable comprises wire rope.
 45. The restraining net accordingto claim 44, wherein the horseshoe cable is secured to the structuralcables by wire rope cable clamps.
 46. A restraining net comprising: top,middle and bottom horizontally extending structural cables; and cableextending substantially horizontally along the horizontally extendingstructural cables in a wave pattern with vertical amplitude, havingpeaks, valleys and midpoints, wherein tangents of the wave midpoints areat least 90 degrees from tangents of the peaks and valleys.
 47. Therestraining net according to claim 46, wherein the structural cablescomprise wire strand.
 48. The restraining net according to claim 46,wherein the top and bottom structural cables comprise wire strand, andthe middle horizontal cable comprises wire rope.
 49. The restraining netaccording to claim 46, wherein the horseshoe cable comprises wire rope.50. The restraining net according to claim 46, wherein the top andbottom structural cables comprise wire strand, the middle horizontalcable comprises wire rope, and the horseshoe cable comprises wire rope.51. The restraining net according to claim 50, wherein the horseshoecable is secured to the structural cables by wire rope cable clamps. 52.A railroad crossing safety system, comprising: first and second energyabsorbing systems installed respectively on each side of a roadway thatintersects railroad tracks; ground retractable restraining means forrestraining automobiles from crossing the railroad tracks, therestraining means extending across the roadway between the first andsecond energy absorbing systems on each side of the railroad tracks;each of the first and second energy absorbing systems comprising:supporting means for providing a rigid support for a fixing means;fixing means for rigidly fixing a vertical axis relative to thesupporting means; shock absorbing means for absorbing forces applied tothe restraining means, the shock absorbing means being mounted on thefixing means to rotate around the vertical axis; and a threshold forcesecuring mechanism connected to the shock absorber preventing expansionof the shock absorber until acted upon by tensile forces of at least aminimum threshold force; wherein the restraining means compriseshorseshoe cable.